\begin{tikzpicture}
    \pgfmathsetmacro{\R}{1.5}
    \pgfmathsetmacro{\r}{\R/2}

    \tkzDefPoints{0/0/O}
    \tkzDefPoint(180:\R){A}
    \tkzDefPoint(0:\R){B}
    \tkzDefPoint(180:\r){O_1}
    \tkzDefPoint(0:\r){O_2}

    \tkzDrawCircle[thick](O,A)
    \tkzDrawArc(O_1,O)(A)
    \tkzDrawArc(O_2,O)(B)
    \tkzDrawSegment[dashed](A,B)
\end{tikzpicture}

